Method and device for the vibrational mechanical activation of composite materials

ABSTRACT

The invention relates to the field of dentistry and can be used for reinforcing composite materials employed when removing various carious and non-carious defects of hard dental tissues in the process of direct or indirect reinforced and un-reinforced composite restorations. The claimed method consists in the vibrational mechanical activation of composite materials by means of vibrationally acting upon a portion of composite material which is applied to the region of a defect. A device for vibrational mechanical activation of a composite material contains at least one working portion for applying a composite material to the region of a defect, said working portion being fixedly attached to a handle connected to a micromotor which creates vibrations which are transferred via the working portion to a layer of composite material by means of distributing same across the entire surface of the defect and achieving the simultaneous superficial plastic deformation thereof.

This application is a continuation-in-part of the United States National stage application of International Application PCT/RU2014/000975 filed on Dec. 23, 2014, which claims the benefit of Russian Patent application No RU 2013147270 Filed on Oct. 23, 2013, the entire disclosure of which is incorporated herein by reference.

FIELD OF INVENTION

The invention relates to the field of dentistry and can be used to repair defects of dental hard tissues of the carious and non-carious origin, in the process of direct or indirect restorations with reinforced and non-reinforced composites.

BACKGROUND

Continuous development of adhesive technologies facilitated popularization of the usage of composite materials in stomatological practice. Currently, there are many chemical and light curing composite materials.

In clinical practice, light-curing composite materials are widely used to repair various defects of dental hard tissues.

Advantages of composite materials

Modern composite materials have high physical and mechanical properties, biological inertness, excellent chemical resistance, low shrinkage factor, stronger adhesion and a better marginal adaptation to the hard tissues of the tooth.

Despite the obvious advantages, composite materials have a number of drawbacks typical to any artificial material used in stomatological practice.

There are a number of complications possible after repairing of defects of dental hard tissues by using composite materials. We distinguish between several classes of the complications that are eliminated in various ways:

Complications of I degree (mild)—the defect of the composite restoration is eliminated by way of polishing or grinding and polishing.

Complications of II degree (medium)—the defect of the composite restoration is eliminated by way of a partial repeated composite restoration.

Complications of III degree (severe)—the defect of the composite restoration is eliminated by way of a full repeated composite restoration.

It is found that micro- and macro-splits take place after the composite restoration. The methods of split curing are described in the article “The criteria for assessing the quality of the restoration after the repairing of defects of the coronal parts of anterior teeth using composite materials and metal mesh-contoured reinforcing framework” by M. L. Melikyan, G. M. Melikyan and K. M. Melikyan//Institute of Dentistry.—2011/2.—Pages 86-88.

A split is a partial destruction of the composite restoration.

Micro-splits are insignificant defects of reinforced and non-reinforced composite restorations, which are eliminated by grinding and polishing. Macro-splits are partial defects of reinforced and non-reinforced composite restorations, which are repaired with composite materials.

One of the main reasons for occurrence of splits of composite restorations is large (critical) defects of the type of pores. The porosity of the composite restorations has different nature.

In fact, porosity is an inherent property of any composite material as such. The degree of porosity of composite materials depends on the following factors:

the quantitative ratio of the monomer and the filler;

the method of preparation of the material (when mixing the material, air bubbles are formed, causing porosity);

the damage of the pre-polymerized filler particles.

Among photopolymer materials, minimal porosity is characteristic of hybrid composites (0.18-2.5%), more porosity is characteristic of micro-filled materials (0.3-3.8%) and maximal porosity is characteristic of traditional materials (0.7-8.4%).

The degree of porosity is increased in the course of restoration. The formation of pores with air bubbles is caused by the manipulations when applying of the composite material during the forming of the composite restoration. The formation of the restoration structure of the tooth consists of adhesion the composite material to the tooth structure and of adhesion fragments of the restorative material (layer-by-layer technique of restoration forming).

During air-oxygen free polymerization of the portions of the composite, the surface layer is polymerized and form strong bond between these portions of the composite. However, due to the interaction of the applied composite material layer surface with air oxygen, diffusing into the composite, non-polymerized layer is formed, which is the so-called “oxygen-inhibited layer”. The layer thickness is of 20-30 microns. The polymerization reaction is not possible in the layer, since the formation of the polymer matrix occurs only through the oxygen bonds, which are already occupied with oxygen in this layer.

If there is a non-polymerized layer between the layers of the composite, then the portions of the composite do not joint to each other, so the junction interface becomes the place of mechanical weakness of the restoration and subsequent dissection of the restoration under the load of chewing. The results of the spectrographic analysis of the sections of the composite materials confirmed the presence of porosities of different nature, filled with air bubbles (see Vestnik of the Dniepropetrovsk University, series “Physics. Radio electronics” 2007, issue 14, No. 12/1).

The classification of pores and their descriptions are given in the article “Analysis of the strength properties of the mesh metal composite materials used in the reinforcement dentistry according to M. L. Melikyan (RDM) (Part I)” by M. L. Melikyan, K. M. Melikyan, S. S. Gavriushin, K. S. Martirosyan, G. M. Melikyan//Institute of Dentistry.—2012/3.—No. 56—Pages 62-63.

The authors distinguish between two types of micro-pores present in the composite restorations:

closed (internal);

open blind (external).

Closed micro-pores are inside the restored tooth:

between the hard tissues of the tooth and the adhesive layer;

between the composite material and the adhesive layer;

within the portion of the composite material;

between the portions of the composite material.

Open blind micro-pores located on the outer surface of the composite restoration.

According to the Griffith's theory, pores are safe at low loads because they do not tend to increase. At high loads, they may be unstable, capable of rapid growth and merging with each other with the formation of major cracks that lead to the destruction of composite restorations.

According to the mechanical principles, the destruction of the material does not occur simply under the load, but because the load causes a concentration of stress energy that is greater than that the material is capable of accumulating.

Given the fact that one of the main causes leading to the occurance of splits of the composite restoration are large (critical) defects according to the type of the pores, so the development of technology that will reduce their number and size and, accordingly, will increase the strength of the composite restoration is an urgent task of dentistry. The solution to this problem will allow reducing the number of complications and prolonging the functional life of the composite restoration. The claimed invention is intended to solve this problem.

The solution to this problem, using the prior art methods, reduces to follow a certain sequence of making the composite restorations. The following recommended steps of adhesion portions of the composite are known:

verification of the presence of a surface layer inhibited by oxygen;

introduction of a portion of the composite material;

control test for adhesion;

plastic processing of the introduced portion of the composite material;

control test;

fixation of the form by directed polymerization;

final polymerization of the portion of the composite material.

It is known from the literature that the main difficulties in applying of the first layer of the composite material to the bottom of the tooth cavity are associated with sticking of the composite to the tool and with the formation of voids between the composite material and the adhesive layer.

Various solutions to this problem were suggested, but it still remains actual (J. SABBAGH “SonicFill system: a clinical approach”/Kerr News/Switzerland—2012, pp. 10-13).

To carry out the plastic processing of the applied portion of the composite material the composite material is spread, with an instrument, over the prepared surface of the tooth hard tissue that has been coated with an adhesive layer, or over the surface of the previously applied layer of the composite so that there are no air bubbles under it.

The whole surface of the applied portion of the composite is processed with a certain pressure using the instrument, which ensures squeezing the oxygen-inhibited layer and adhesion the portion of the composite to the surface at a certain point, which is under pressure at this moment.

The technique of reducing the porosity of the composite material, that is implemented in the known method, consists of “burnishing” the portion of the composite material by way of the surface plastic deformation, using a sliding tool, over the locally contacting it surface of the deformable material (“Composite, filling and facing materials”. A.V. Borisenko and V.P. Nespryadko, Kiev, Kniga Plus, 2001). This method does not provide the maximal squeezing of air with the tool out of the pores of the applied composite layer surface.

The disadvantage of this method is that during its implementation the pores are redistributed, as a rule, within the material due to their displacement by the smoothing mechanical action of the tool. At the same time, the insignificant squeezing of the air out of the pores is non-uniform over the entire surface of the deformable material due to the lack of the uniformly controlled force impact of the restoration tool upon the surface of the applied composite material.

In order to reduce porosity and to increase the strength of the composite material, the method of manual mechanical activation (MMA) of the composite material according to M.L. Melikyan is currently used.

Mechanical activation of the composite material means mechanical impact upon the composite material, which leads to an improvement of its physical and mechanical properties.

This method is described in the Russian patents No. 2238696 and No. 2331385, the patent owners are M.L. Melikyan, G.M. Melikyan, K.M. Melikyan.

The essence of the invention according to patent No. 2238696 lies in that the missing coronal part is restored taking the anatomical-topographical and biomechanical peculiarities of the structure of the tooth, which is being restored, using a reinforced mesh metall-composite into account.

To restore the missing enamel layer, the composite material is roll-shaped by way of manual manipulation by fingers in gloves having textured surface of natural latex without powder. Then, the rolls shaped in this way are used to restore missing walls of the crown part of the tooth.

The essence of the invention according to Russian patent No. 2331385 lies in the fact that when repairing the defect of the cutting edge up to the depth of 2 mm during the restoration, the composite material is subjected to manual manipulation, too, when shaping the composite roll.

The patent owners together with scientists from the Bauman Moscow State Technical University investigated the effect of the method of manual mechanical activation (MMA) upon the strength properties of the composite material. The laboratory studies were conducted using the universal testing machine Galdabini Quasar 50.

The tests were conducted using samples with the dimensions of: length (l) 45 mm, height (a) and width (b) equal to 5 mm for static three-point bending according to the principle: “The concentrated load is applied in the middle of the span”. During the tests, the diagram data on the load deformation - the maximum sag was read, as well as the failure load FP (N), was determined.

To test the static three-point bending, samples of 3 series of the composite material were made in total amount of 15 pieces (5 pieces in each series). All series of the samples were made at room temperature and were kept in water after their manufacture till the test.

Series I (control series): the portions of the composite material (0.5 g) were measured out by extruding the material out of a syringe, weighed, and introduced into the mould without subjecting to any additional mechanical impact (mechanical activations). To produce samples of series I using a metal plastic instrument, a portion of the composite material was extruded out of the syringe and 0.5 g was weighed, and then the portion was placed on the bottom of a polypropylene mould and uniformly distributed over the whole bottom of the mould using an instrument. Given that the sample was 45 mm long, each composite layer was polymerized 3 times for 20 seconds longwise the polypropylene form, thus the polypropylene form was sequentially filled with the composite material layer by layer and polymerization was carried out.

The ready sample was removed from the mould and control polymerization was carried out from the external surfaces. The weight of the samples was measured using scales with the accuracy of ±0.01 g; the geometric dimensions of the samples were measured with an electronic calliper with the accuracy of ±0,01 mm

Series II: portions of the composite material (0.5 g) were measured by extruding the material out of a syringe and weighed, and then shaped in the form of balls using the method of manual mechanical impact (mechanical activation). The formed composite balls were put into the mould. In order to make samples of series II using a metal plastic instrument, a portion of the composite material was extruded out the syringe and 0.5 g was weighed. Then, the composite material (with the method of mechanical activation) was shaped as balls using the rotational movements of the fingers in medical diagnostic disposable gloves with the textured surface made of natural powder-free latex.

Next, the formed composite ball was placed on the bottom of the polypropylene form and, using an instrument, it was evenly distributed all over the bottom and polymerization was carried out.

Thus, the polypropylene mould was filled with the composite material sequentially layer by layer. The ready sample was removed from the mould and the control polymerization was carried out from the external surfaces. Further, the weight and revised geometric dimensions of the samples were measured with the accuracy of ±0,01 mm In the process of measuring, the arithmetic mean values of the sample length, width and thickness were used.

Series III differed from series II in that the rolls were formed of the obtained balls (by using the method of mechanical activation). The formed composite rolls were placed into the mould. In order to make samples of series III using a metal instrument a portion of the composite material was extruded out the syringe and 0.5 g of the composite material was weighed. Afterwards, using the rotational movements of the fingers in medical diagnostic gloves, the composite material (by applying the method of mechanical activation) was shaped as balls, and then as rolls. Next, the formed composite roll was placed on the bottom of the mould, and evenly distributed all over the bottom using an instrument and polymerization was carried out.

Thus, the polypropylene mould was filled with the composite material sequentially layer by layer. Ready sample was removed from the mould and the control polymerization was carried out from the external surfaces. Further, the weight was measured and the revised geometric dimensions of the samples were measured with the accuracy of ±0,01 mm In the process of measuring, the arithmetic mean values of the sample length, width and thickness were used.

Each sample was assigned a serial number and arrows were used to indicate the direction of the load application.

Samples of I-III series were tested for static three-point bending at the temperature of 20° C.

The maximum force generated by the machine is 500 N.

The comparative results, of testing strength characteristics by static three-point bending of the composite samples of series I-III, depending on the testing method, are shown in Table 1.

TABLE 1 Comparative results of the failure force for samples of series I-III made of micro-hybrid composite material Sample series Series I Series II Series III Methods of Control sample Test sample in Test sample in making samples made without the form of a the form of a mechanical composite ball composite roll activation made with made with mechanical mechanical activation activation Maximum load 168.58 178.28 180.92 F_(max) [N]

The test results for the static three-point bending of the composite samples made of the micro-hybrid composite material, revealed that when the composite material is shaped in the form of a ball (using the method of mechanical activation) the limit load of the sample is increased by 5.7% in comparison with control samples.

By shaping the composite material in the form of a roll (using the method of mechanical activation), the limit load of the sample increases by 7.3% in comparison with control samples (without a roll).

The tests have confirmed that the method of manual mechanical activation of the composite material decreases:

porosity by 30%;

the maximum pore size (critical defects) by 45%;

the mean pore size by 3%.

The disadvantage of this method of manual mechanical activation lies in that shaping the composite material in the form of a roll in the course of the restoration is applied mainly during the restoration of missing walls of the crown part of the tooth, or during the repairing defects in the cutting edge of the tooth. That is, this method of mechanical activation is used to eliminate some specific defects.

The effect of increasing the strength of the composite restoration, achieved by using the known method, is not sufficient to obtain monolithic composite restoration (MCR). The claimed method of reducing porosity and increasing the strength of the composite material is based on the use of a fundamentally new method of its hardening with vibrational mechanical activation (VMA).

In the course of the repairing defects of dental hard tissues using the composite material by way of applying the claimed method, the layers of the composite material are subjected to vibrational impact (vibrational surface plastic deformation). In the process of implementation of the claimed method, each subsequent layer is subjected to vibrational impact prior to its polymerization.

Vibrational surface plastic deformation is vibrational surface plastic deformation of the material due to mechanical vibration of the tool (GOST 18296-72. Surface working. Terms and definitions).

The authors of the invention together with scientists of Bauman Moscow State Technical University conducted studies on the effect of vibrational mechanical activation (VMA) of the composite material on the strength properties of this composite material using test methods described above.

Samples of series I (control samples) made as described above, and samples of series II, which differ from control samples in that during their manufacture each applied layer of the composite material was subjected to vibrational impact with the oscillation frequency of 1000 Hz before polymerization, were tested.

TABLE 2 Comparative results of the failure force for samples of series I-II made of micro-hybrid composite material Sample series Series I Series II Methods of Control sample made Test sample in the form of a making samples without mechanical composite roll made with activation mechanical activation Maximum load 168.58 206.5 F_(max) [N]

The test results for the static three-point bending of the composite samples of series I and II revealed that the limit load of the samples of series II, made of the micro-hybrid composite material, which was subjected to vibrational impact, increased by 22.5% in comparison with the control samples of series I.

As a result of the subsequent tests conducted together with scientists of the Kazan Federal University (KFU), the dependence of the load limit increase upon the degree of porosity of the micro-hybrid composite material was identified.

In comparison with the control samples of series I, the samples of series II subjected to vibrational mechanical activation feature:

reduction of porosity of the micro-hybrid composite material by 70%;

reduction of the maximal pore size (critical defects) by 45%;

reduction of the mean pore size by 3%.

In the samples of series II, subjected to vibrational mechanical activation, there are no boundaries at the junction interface between the layers of the composite material.

The advantages of the method of vibrational mechanical activation (VMA) of the composite material according to M.L. Melikyan are as follows:

the load limit increases by 22.5% (without introduction of additional reinforcing elements into the composite material in the process of restoration);

porosity decreases by 70%;

the maximal pore size (critical defects) decreases by 45%;

the mean pore size decreases by 3%.

The method of vibrational mechanical activation of the composite material is used:

to repair any defects of dental hard tissues;

for direct, indirect, reinforced and non-reinforced composite restorations.

The method of vibrational mechanical activation of the composite material ensures:

constant controlled force of the vibrational impact by the restoration tool upon the portion of the composite material and its uniform distribution over the entire defect surface, which was subjected to adhesive processing, or upon the surface of the previously deposited and polymerized composite layer;

the specified direction of vibration impact into the treated surface—perpendicular to the surface of the adhesive layer or the previous layer of polymerized composite material;

effective air squeezing out of the pores (rather than pores redistribution from the surface of the previously deposited composite layer), and filling them with the composite material;

a significant reduction in the size of critical defects, which reduces the probability of appearance of splits of the composite restoration;

dense and durable adhesion of the composite material to the adhesive layer and to each subsequent portion of the composite material;

forming a solid sealed monolithic composite structure;

effective marginal adaptation of the composite material to the hard tissues of the tooth, which helps reduce micro-leakages and the formation of secondary caries.

The method of vibrational mechanical activation of the composite material decreases:

the probability of complications and prolongs the operational life of the composite restoration;

retention of dyes by reducing the number and size of open blind micro-pores on the surface of the composite restoration, which ensures high aesthetic quality of the composite restoration;

sorption of water and the formation of bacteria colonies;

the probability of occurrence of pores between the adhesive layer and the composite material, and between the layers of the composite material as the composite material does not stick to the tool;

the arm muscles tension, which occurs when the force from the hand is transmitted through the tool to a portion of the composite material, is excluded.

The application of the method of vibrational mechanical activation of the composite material allows to:

performing restoration without eye and finger strain, including in not easily accessible areas of the tooth;

shortening the time necessary for the composite restoration due to the effective adhesion of the portion of the composite material to the adhesive or composite layer.

The method of vibrational mechanical activation of composite materials according to M.L. Melikyan is implemented as follows. When repairing a defect of the crown part of the tooth or when eliminating complications of the composite restoration (of degree II and III), known methods of layer-by-layer restoration/reconstruction of the crown part of the tooth are applied using the composite materials, which methods have been described, including in the Russian patents for inventions, issued to patent owners M. L. Melikyan, G. M. Melikyan and K. M. Melikyan (No. 2273465, No. 2331386, No. 2403886, and No. 2403887). When implementing the known techniques of layer-by-layer applying of composite materials, each subsequent layer of the applied composite material is subjected to vibrational mechanical activation for 20 seconds with the vibration frequency of up to 1000 Hz before polymerization. The permissible level of vibration corresponds to the Sanitary Regulations and Norms (SanPiN), approved by Decree No2 of the Goskomsanepidemnadzor State Committee for Sanitary Supervision and Disease Control of the Russian Federation on Jan. 19, 1996.

For the implementation of the claimed method, a special device for vibrational mechanical activation of the composite material is used.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of this invention will be had by now referring to the accompanying drawings in which:

FIG. 1 is a view of a first embodiment of the special device for vibrational mechanical activation of the composite material crowns in accord with the present invention;

FIG. 2 is a view of a second embodiment of the special device for vibrational mechanical activation of the composite material crowns in accord with the present invention;

DETAILED DESCRIPTION OF THE INVENTION

The device (FIG. 1 and FIG. 2) comprises a handle 1, for example, in the form of a tubular body, at one end or at both ends of which one or two working elements 2 are fixedly attached and used for applying a portion of the composite material to the defect area of the crown part of the tooth and its distribution over the defect surface by means of vibrational impact. The design of working elements 2 is similar to the working element of the known plastic instrument.

The handle 1 includes a fixing means—framework 3 for fixing the battery power supply 6 and a micro-motor 5, which is connected to the power supply 6 and generates vibration. There is a button 4 of the actuating element placed on the handle 1 for switching the power supply 6 on by pressing the button 4.

The embodiments of the device provide for placing the power supply 6 and the micro-motor 5 both outside the handle 1 (FIG. 1) or both inside the tubular body 1 (FIG. 2).

In order to fix the power supply 6 and the micro-motor 5 outside the body, a removable framework 3 with finger grips is used as the fixing device. The battery power supply 6 and the micro-motor 5 are fixed internally on the framework 3.

In the embodiment (FIG. 2) with the location of the framework 3 inside the tubular body 1, a window may be provided in the inner wall of the tubular body 1, for the internal placement of the battery power supply 6 and of the micro-motor 5. The framework 3 is fixed in a window opening by interference fit.

In cases of the internal and external placement of the framework 3, the framework 3 serves as the cover insulating the battery power supply 6 and the micro-motor 5 from the external environment. In case the battery power supply 6 should be replaced, the framework 3 is taken out, the spent battery is removed and replaced with a new one.

The device for vibrational mechanical activation of the composite material operates as follows.

A portion of the composite material is applied, using the working element 2, to the surface in the area of the defect of the crown part of the tooth.

By means of the actuating element button 4, the power supply 6 is switched on and electrically connected to the micro-motor 5. The activated micro-motor 5 generates vibrations that are transmitted to the working element 2, whereby vibrational mechanical activation of the deposited layer of the composite material is performed. The composite material is distributed under the impact of this vibration over the entire surface of the defect and is simultaneously subjected to surface plastic deformation for no less than 20 seconds. Then, using the activating element button 4, the power supply 6 is switched off. The device returns to the static condition and is ready for the application of the next portion of the composite material.

After the vibrational impact has been completed, the layer of the composite material that has been subjected to the vibrational mechanical activation is polymerized in a conventional manner.

Then, a new portion of the composite material is applied, which is subjected to vibrational mechanical activation in accordance with the procedure described above. The operations of applying portions of the composite material, the vibrational impact and polymerization are repeated until the full restoration of the tooth hard tissues integrity. While the invention has been particularly shown and described as referenced to the embodiments thereof, those skilled in the art will understand that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention. 

1. A method of vibration mechanical activation of composite materials in direct and indirect composite restorations of teeth comprising applying a vibrational impact before polymerization to every portions of the composite materials, which applied to an area of a defect.
 2. The method according to claim 1, wherein the vibrational impact on the portions of composite material is performed with an oscillation frequency up to 1000 Hz.
 3. The method according to claim 1, wherein the portions of composite material are subjected to the vibrational impact for at least 20 seconds.
 4. A device for vibrational mechanical activation of composite material, comprising at least one working part for application of composite material to a defect area, a handle, a battery power supply, a micromotor, wherein the working parts are fixedly attached to the handle, the handle is provided with an activating element button for actuation of battery power supply, said battery power supply electrically connected to the micro motor, said micro motor generates vibrations, said vibrations are transmitted on every portions of composite material by the way of distributing the vibration on an entire defect surface and simultaneous surface plastic deformation.
 5. The device according to claim 4, wherein the battery power supply and micro motor are placed in a framework, said framework are fixedly attached with capability of removal on the handle.
 6. The device according to claim 4, wherein the handle is formed as a tubular body,
 7. The device according to claim 6, wherein the battery power supply and micro motor are placed inside the tubular body. 